The present invention relates to an apparatus and method for embedding connector plates in wooden structural members and, more particularly, to an assembly machine having a plurality of work stations at which connector plates are pressed into opposite sides of wooden structural elements. Specifically, this invention relates to an assembly machine and method for embedding connector plates in the joints of wooden frame structures such as furniture frames and roof trusses.
Prefabricated wooden frames have been developed in the prior art to facilitate the rapid and convenient assembly of furniture frames and roof trusses. Such frames usually include a plurality of wooden framing members with the joints of the frames fastened together by connector plates. Typically, each connector plate is provided with a relatively large number of elongated nail-like teeth struck therefrom which are embedded in adjacent framing members at the joints of the frame. See, for example, plates of the type disclosed in U.S. Pat. No. 2,877,520 assigned to the same assignee of the present invention.
Various machines have been developed in the prior art for pressing connector plates into wooden members. See, for example, U.S. Pat. No. 3,419,205, assigned to the common assignee herewith, which discloses an apparatus for reinforcing lumber elements, such as railroad ties, by embedding connector plates at the ends of the lumber elements. The machine includes a horizontal clamp pressure platen and a vertical clamp pressure platen for pressing connector plates into the horizontal and vertical surfaces at the end of a lumber element which is rectangular in cross section. In addition, U.S. Pat. No. 3,805,694, assigned to the common assignee herewith, discloses a fluid actuated press for embedding connector plates into the joints of wooden trusses which includes a base including a lower press platen and a floating head including an upper press platen operable by a fluid actuated cylinder carried by the head for moving the head toward and away from the base. The press includes a mechanical linkage coupled to the fluid actuated cylinder to enhance the mechanical advantage at the press platens. Other patents showing similar types of machines are U.S. Pat. Nos. 3,602,237, 3,603,244 and 3,910,512, all of which are assigned to the same assignee as the present application.
Depending on the type of connector plates and wooden members employed in the frame, the assembly machines may be required to produce extremely large forces to embed the teeth of the connector plates into the wooden elements. The amount of force is primarily determined by the wood density, tooth size, and number of teeth per joint. For example, in the case of large trusses, forces up to 80 to 100 tons may be required to embed the connector plates into the wooden structural elements.
A major concern in the application of such large forces to the connector plates is uniform force distribution to avoid distortion of the plates and ensure complete insertion of the nail-like teeth into the wooden members. These requirements are critical to produce strong and permanent frame joints. To achieve the desired uniform force distribution, it is necessary for the press platens to maintain essentially uniform contact with the connector plates and wooden structural elements while the force is applied. The requirement is extremely important in the case where a pair of connector plates is driven simultaneously into opposite sides of the wooden structural elements.